The invention relates to a method of storing a disc-ID on a record carrier comprising tracks in which information can be stored, said disc-ID comprising a predetermined number of disc-ID bits.
The invention also relates to a device for reading a record carrier, comprising a system for detecting and reading information present on the record carrier, the system comprising detection means for detecting a disc-ID on the record carrier, said disc-ID comprising a predetermined number of disc-ID bits.
The invention also relates to a device for writing a record carrier, comprising write means for inducing a detectable change on a layer of the record carrier, the write means being further adapted to write a disc-ID on the record carrier, said disc-ID comprising a predetermined number of disc-ID bits.
The invention further relates to a record carrier comprising a disc-ID stored on the record carrier, said disc-ID comprising a predetermined number of disc-ID bits.
The method according to the invention may be used in various types of generally known record carriers such as, for example, CD-R, DVD+RW, MO-disc.
Since the literature uses a plurality of terms for disc-IDs, such as identifier, disc-identifier, ID, disc code, identification tag, it will be noted for the sake of clarity what is to be understood by disc-ID in the description of this invention. The disc-ID consists of information of a predetermined bit length, stored on a record carrier, with the purpose of being able to distinguish this record carrier from other record carriers of the same type.
It should be clear from the above that the disc-ID of a record carrier is comparable with, and may perform the same function as, finger prints. It is important that the presence of a disc-ID provides the possibility of distinguishing individual record carriers from each other and not only the type of record carrier (for example, CD-ROM, CD-R or CD-RW).
The method according to the invention is not limited to circular record carriers but may also be used in non-circular record carriers such as tapes and cards.
The registration of a unique disc-ID on a record carrier is important for different reasons. European patent application EP 0 785 547 A2, hereinafter referred to as document D1, states, as an advantage of registering a unique disc-ID, that a computer system using these record carriers can keep track of a list of errors present on various record carriers. The system can then easily detect when a given record carrier does not function or should be replaced or copied. The registration of a disc-ID on a record carrier may also be important in a method of cryptocommunication. In this case, the disc-ID is used for providing, together with keys (for example, what is referred to as shared secret) present in a recorder or player, access to encrypted information on the record carrier. The use of a disc-ID on a record carrier is also recommendable in the field of copy protection, because copy protection is considerably simplified when individual record carriers can be distinguished from each other. To make this possible, each record carrier receives a unique identification code, the disc-ID. By means of this disc-ID, the data (for example, Audio/Video (A/NV) data) is coupled to the physical medium, i.e. the record carrier.
A method of the type described in the opening paragraph is known, inter alia, from document D1. This document describes a method of storing one disc-ID (whose letters ID stand for identification) on a record carrier. If there is no disc-ID on the record carrier, a unique disc-ID is generated for this purpose and registered on a reserved area of the record carrier. When an MO disc is used, an unused sector in the defect management area (DMA) may be used as a reserved area. When a CD-R is used, the table of contents (TOC) in the lead-in zone may be used as a reserved area.
The disc-ID as described in document D1 is registered on a reserved area of the record carrier. The disc-ID is thus vulnerable to attempts of hacking and removing the disc-ID. Not only will it be easy to find a disc-ID registered in a reserved area on a record carrier, but it will also be easy to remove this disc-ID, for example, by giving all the bits constituting the disc-ID the same binary value. Moreover, it will be easier to make a number of discs all of which have the same disc-ID so that they cannot be distinguished from each other.
It is an object of the invention to realize a reliable disc-ID on record carriers, which is difficult to trace and remove.
To this end, the method according to the invention is characterized in that the disc-ID bits are stored on the record carrier in a scattered way.
The invention is based, inter alia, on the recognition that, by storing the disc-ID bits on the record carrier in a scattered way, it will be more difficult to trace the entire disc-ID and possibly remove it. Storage of the bits on the record carrier in a scattered way is understood to mean that one disc-ID is stored in a number of portions of limited bit size on the record carrier. Overwriting such a portion with a limited bit size is not easy and overwriting a single bit is not very well possible with the current equipment (for example, the CD-R and CD-RW recorders). A minimum bit size which can be realized in a single write action is of the order of several tens of bits, for example, 32 bits. The ratio between this minimal bit size and the size of the entire disc-ID is, for example, 20%. This corresponds to a disc-ID of 160 bits (5xc3x9732 bits). By scattering the different disc-ID bits on the record carrier in groups which are smaller than this minimal bit size, the disc-ID will be difficult to remove. This has, inter alia, the advantage that, if the disc-ID forms part of a copy protection system or of a system for crypto communication, these systems will be more reliable and can less easily be hacked.
Another embodiment is characterized in that the disc-ID bits are stored in groups of one bit on the record carrier in a scattered way.
By storing the disc-ID bits on the record carrier in a scattered way in groups of one bit, it will be more difficult to trace the entire disc-ID and possibly remove it.
A further embodiment is characterized in that the disc-ID bits are stored at positions reserved for storing non-data bits.
It is known that a number of bits (referred to as non-data bits) is not used for storing data on a number of types of frequently used record carriers, but have different other reasons for their presence. For example, in the description of the standard physical format of the Audio-CD (referred to as the Red Book), non-data bits are defined, inter alia, as error correction bits, merging bits and sync bits. For details, reference is made to the standard format of the Audio-CD (see International Standard IEC 908).
It is also clear from the foregoing that the data capacity of the record carrier is reduced if the disc-ID is stored on a reserved area of the record carrier where data can also be stored. By using the non-data bits for storing the disc-ID bits, a disc-ID is realized which does not result in a reduction of the total data capacity of the record carrier.
Moreover, it is to be noted that the disc-ID bits can also be stored at positions which, in accordance with the description of the standard physical format of the relevant record carrier, do not fulfill a function. These positions are suitable because the value of the bits at these positions can be freely chosen. This freedom provides the possibility of storing any desired disc-ID on the record carrier.
Another embodiment is characterized in that the disc-ID bits are stored in a preamble of the data bits on the record carrier.
By storing the disc-ID in the preamble of the data bits on the record carrier, the disc-ID is stored on a reserved area of the record carrier, where only non-data bits are stored. The data capacity of the record carrier is not reduced thereby. For a description of the preamble of the data bits and its function, reference is made to the description of the Figures.
A further embodiment is characterized in that the disc-ID bits associated with one disc-ID are stored in a predetermined number of tracks.
The different tracks on a record carrier are provided with a number so that the information in the tracks can be retraced. By storing the disc-ID bits associated with one disc-ID in a predetermined number of tracks, it will be easier and faster to retrace and read the disc-ID because it will be easy to find the start of the disc-ID with reference to the track number to be read.
Yet another embodiment is characterized in that the same number of disc-ID bits is stored in the tracks.
Information is stored in so-called tracks on different types of record carriers. Generally, a track comprises a portion comprising, inter alia, the address of this track, followed by a portion in which information can be stored. The different tracks on a record carrier are provided with a number so that the information present in the tracks can be retraced. By storing the same number of disc-ID bits in each track, retracing and reading of the disc-ID will be simpler and faster. For storing, for example, a 160-bit disc-ID, 20 tracks are required for storing the disc-ID when eight disc-ID bits are stored in each track.
A further embodiment is characterized in that a disc-ID can be stored several times on the record carrier.
It will be evident that, if the disc-ID is present on a record carrier only once, damages of the record carrier at the location where the disc-ID is registered may lead to loss of this disc-ID. This also applies to the case where the disc-ID consists of disc-ID bits which are stored on the record carrier in a scattered way. The moment the disc-ID is no longer readable from the record carrier, the information which may be present on the record carrier in an encrypted form is no longer accessible if the disc-ID bit is used for providing access to information of this type. The registration of a plurality of disc-IDs whose disc-ID bits are stored on the record carrier in a scattered way reduces the risk that there is no readable disc-ID left on the record carrier.
A further embodiment is characterized in that the same number of tracks is used for storing the disc-IDs.
By using a constant number of tracks for storing a disc-ID, retracing and reading of the disc-ID bits will be simpler and faster. With reference to the numbers of the tracks on the record carrier, it can then be easily determined which disc-ID bits are present in which track.
Another embodiment is characterized in that a disc-ID byte is formed by eight disc-ID bits having the same position in a direction perpendicular to a read direction of the record carrier.
By causing disc-ID bits having the same position in a direction perpendicular to a read direction of the record carrier to form a disc-ID byte, the effect of errors is reduced. In fact, the errors fall within one byte in the case of damage. When a circular record carrier is used, the disc-ID byte is formed by eight disc-ID bits having the same tangential position. Since, in the case of error correction, this error correction is preferably performed at byte level, a local damage having a size of eight tracks in the tangential position will result in one byte with eight errors. If the disc-ID bytes are formed in the sequence in which the disc-ID bits are read from the record carrier (i.e. in the sequence in which also the data are read from the record carrier), a local damage having a size of eight tracks in the tangential position will result in eight bytes with one error each.
The device according to the invention is characterized in that the detection means are also adapted to detect a disc-ID whose disc-ID bits are stored on the record carrier in a scattered way.
Another device according to the invention is characterized in that the write means are also adapted to write the disc-ID bits on the record carrier in a scattered way.
The record carrier according to the invention is characterized in that the disc-ID bits are stored on the record carrier in a scattered way.